Learn about the quality of rainwater stored in tanks and other health issues related to RWH.
While rainwater quality will not always reach WHO or national drinking-water standards, when compared with most unprotected, traditional water sources, rainwater from wellmaintained roof catchments usually represents a considerable improvement and is generally safe to drink without treatment.
Except in heavily urbanized and industrialized areas or regions adjacent to active volcanoes, atmospheric rainwater is very pure and any contamination of the water usually occurs after contact with the catchment system. Rainwater from ground catchment systems is not recommended for drinking unless first boiled or treated.
A degree of chemical and microbiological contamination of roof rainwater runoff is inevitable, but this will not generally cause a problem if the roof, gutters and storage tank are properly maintained and regularly cleaned and inspected.
Reports of disease outbreaks linked to roof water sources are rare. A few cases of gastrointestinal illnesses linked to large quantities of bird or animal droppings on the roof have been reported, and appropriate measures should be taken to reduce these risks.
The chemical and physical quality of stored rainwater is normally high. Care should be taken to avoid any possible sources of lead or other heavy metals, e.g. from lead flashings or lead-based roof paints.
Rainwater tanks can provide breeding sites for mosquitoes, which in some areas act as vectors for diseases such as dengue fever, yellow fever and malaria. It is therefore essential that any openings to the tank are fully screened.
To protect water quality, good system design, operation and maintenance are essential. Water quality will generally improve during storage, provided light and living organisms are excluded from the tank, and fresh inflows do not stir up any sediment.
The use of filters and first-flush diverters can further improve the rainwater quality. Further treatment through boiling, exposure to sunlight or ultraviolet radiation and chlorination can be undertaken if there are concerns over the water quality.